1. Field of the Invention
The present invention relates to a photometric apparatus including a plurality of photometric sensors.
2. Description of the Prior Art
In a photometric apparatus of an single-lens reflex camera, a photometric sensor is disposed on the exit surface side of a viewfinder optical system, e.g., in the vicinity of the exit surface of a pentagonal prism, to measure the brightness of an object image on a focusing screen by re-forming the same object image on a light receiving surface of the photometric sensor. Additionally, a split photometric sensor in which a light receiving surface thereof is divided into a plurality of photometric areas to measure the brightness of an object image incident on each of these photometric areas is known in the art. In this split photometric sensor, the plurality of photometric areas are isolated from one another by an insensitive area on the light receiving surface, and accordingly, the brightness of an object image incident on the insensitive area does not contribute to the photometric measurement of the split photometric sensor.
Accordingly, the assignee of the present invention has proposed a photometric apparatus including a pair of split photometric sensors, wherein each of the pair of split photometric sensors includes a plurality of split sensing areas and an insensitive area, and wherein portions of the object image which are formed on the insensitive area of one of the pair of split photometric sensors are formed on the plurality of spit sensing areas of the other split photometric sensor. This photometric apparatus is disclosed in Japanese Unexamined Patent Publication H11-133477.
Since this photometric apparatus has two different photometric optical systems for the pair of split photometric sensors, the volume necessary for accommodating these elements is great, and accordingly, there are many factors of error due to the existence of more than one photometric optical system. Specifically, errors or fluctuations easily occur in the output characteristics peculiar to full-aperture photometering respect to the f-number because more than one incidence optical system exits. Because of the existence of more than one photometric optical system, it is necessary for each photometric optical system to set an optimum correction factor for correcting error during full-aperture photometering, which causes an increase in memory capacity for storing software of a controller dealing with these optimum correction factors and complicates the examination of the correction factor settings. Moreover, if the plurality of photometric optical systems are made independently of each other on the grounds that it is difficult for the plurality of photometric optical systems to be made as a single unit, the number of manufacturing steps is increased.